Circuit devices with gate seals

ABSTRACT

Various examples of a circuit device that includes gate stacks and gate seals are disclosed herein. In an example, a substrate is received that has a fin extending from the substrate. A placeholder gate is formed on the fin, and first and second gate seals are formed on sides of the placeholder gate. The placeholder gate is selectively removed to form a recess between side surfaces of the first gate seal and the second gate seal. A functional gate is formed within the recess and between the side surfaces of the first gate seal and the second gate seal.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 17/321,730, filed May 17, 2021, which is adivisional of U.S. patent application Ser. No. 16/124,451, filed Sep. 7,2018, which claims the benefit of U.S. Provisional Application No.62/592,571, entitled “Circuit Devices with Gate Seals” and filed Nov.30, 2017, each of which is incorporated herein by reference in itsentirety.

BACKGROUND

The semiconductor industry has progressed into nanometer technologyprocess nodes in pursuit of higher device density, higher performance,and lower cost. Beyond merely shrinking devices, circuit designers arelooking to novel structures to deliver even greater performance. Oneavenue of inquiry is the development of three-dimensional designs, suchas fin-like field effect transistors (FinFETs). A FinFET may beenvisioned as a typical planar device extruded out of a substrate andinto the gate. An exemplary FinFET is fabricated with a thin “fin” (orfin structure) extending up from a substrate. The channel region of theFET is formed in this vertical fin, and a gate is provided over (e.g.,wrapping around) the channel region of the fin. Wrapping the gate aroundthe fin increases the contact area between the channel region and thegate and allows the gate to control the channel from multiple sides.This can be leveraged in a number of way, and in some applications,FinFETs provide reduced short channel effects, reduced leakage, andhigher current flow. In other words, they may be faster, smaller, andmore efficient than planar devices.

As a further example, developments have been made to the gate structuresof transistors in integrated circuits. At a high level, a gate structuremay include a conductor and a gate dielectric that separates theconductor from a channel region of the transistor. With respect to thegate conductor, developments now allow the use of layers of metal as asubstitute for polysilicon in the gate conductor. Accordingly, whereaspolysilicon once replaced metal as a gate conductor because ofpolysilicon's increased resistance to heat and ease of fabrication,metal is once again replacing polysilicon in part because of metal'shigher conductance.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIG. 1 is a perspective view of a portion of a workpiece according tosome embodiments of the present disclosure.

FIGS. 2A and 2B are flow diagrams of a method of fabricating a workpieceaccording to some embodiments of the present disclosure.

FIGS. 3A, 4A, 5A, 6A, 7A, 8A, 9A, 10A, 11A, 12A, 13A, 14A, and 15A arecross-sectional view diagrams of the workpiece taken through a fin atvarious stages of a method of fabricating a workpiece with a gate sealaccording to some embodiments of the present disclosure.

FIGS. 3B, 4B, 5B, 6B, 7B, 8B, 9B, 10B, 11B, 12B, 13B, 14B, and 15B arecross-sectional view diagrams of the workpiece taken through a non-finregion at various stages of a method of fabricating a workpiece with agate seal according to some embodiments of the present disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the disclosure.Specific examples of components and arrangements are described below tosimplify the present disclosure. These are, of course, merely examplesand are not intended to be limiting. For example, the formation of afirst feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations beyond the extentnoted.

Moreover, the formation of a feature on, connected to, and/or coupled toanother feature in the present disclosure that follows may includeembodiments in which the features are formed in direct contact, and mayalso include embodiments in which additional features may be formedinterposing the features, such that the features may not be in directcontact. In addition, spatially relative terms, for example, “lower,”“upper,” “horizontal,” “vertical,” “above,” “over,” “below,” “beneath,”“up,” “down,” “top,” “bottom,” etc. as well as derivatives thereof(e.g., “horizontally,” “downwardly,” “upwardly,” etc.) are used for easeof the present disclosure of one features relationship to anotherfeature. The spatially relative terms are intended to cover differentorientations of the device including the features.

As device sizes continue to fall, raised features present an increasingchallenge to fabrication. For example, as the name implies, FinFETs aretransistors where the gate wraps around a raised fin. As fins narrow andthe gaps between fins become smaller, it may prove difficult to reliablyfabricate the gates surrounding the fins, particularly in, but notlimited to, the trenches between fins. In a gate replacement processwhere a temporary placeholder gate is formed and later replaced with ametal-containing functional gate, defects such as metal gate extrusionmay occur in the trenches and elsewhere when the functional gate isformed.

To address this issue and others, some embodiments of the presentdisclosure provide a transistor with a gate seal to prevent extrusionand other defects. In one such embodiment, a placeholder gate is formedaround the channel region of a fin. A gate seal is formed on theplaceholder gate prior to forming a gate spacer around the placeholdergate. The gate seal provides a barrier around the placeholder gate,including in areas where the gate spacer may not be effectively anduniformly deposited such as the trenches between fins. When theplaceholder gate is removed, the gate seal is left in place to providean effective barrier against gate extrusion when forming the functionalgate.

In some embodiments, because the gate seal is formed by a process thatprovides more uniform deposition within the trench than the depositionprocess used to form the gate spacer, the gate seal reduces defects.Furthermore, the gate seal may reduce the surface roughness of theplaceholder gate and thereby provide a better surface for the gatespacer to adhere to. In turn, this may improve the uniformity of thegate spacer. Thus, some embodiments of the present disclosure reducegate defects, particularly in trenches between fins, in order to improveyield. However, unless otherwise noted, no embodiment is required toprovide any particular advantage.

FIG. 1 is a perspective view of a portion of a workpiece 100 accordingto some embodiments of the present disclosure. FIG. 1 has beensimplified for the sake of clarity and to better illustrate the conceptsof the present disclosure. Additional features may be incorporated intothe workpiece 100, and some of the features described below may bereplaced or eliminated for other embodiments of the workpiece 100.

The workpiece 100 includes a substrate 102 with one or more device fins104 formed upon it and separated by isolation features 106. The devicefins 104 are representative of any raised feature, and while theillustrated embodiments include FinFET device fins 104, furtherembodiments include other raised active and passive devices formed uponthe substrate 102. In some embodiments, the FinFET device fins 104include a pair of opposing source/drain features 108 separated by achannel region 110. The flow of carriers (electrons for an n-channelFinFET and holes for a p-channel FinFET) through the channel region 110is controlled by a voltage applied to a gate stack 112 adjacent to andoverwrapping the channel region 110. One of the gate stacks 112 is shownas translucent to better illustrate the underlying channel region 110.

In the illustrated embodiment, the channel region 110 rises above theplane of the substrate 102 upon which it is formed and above theisolation features 106, and accordingly, circuit devices formed on thedevice fins 104 may be referred to as a “nonplanar” devices. The raisedchannel region 110 provides a larger surface area proximate to the gatestack 112 than comparable planar devices. This strengthens theelectromagnetic field interactions between the gate stack 112 and thechannel region 110, which may reduce leakage and short channel effectsassociated with smaller devices. Thus in many embodiments, FinFETs, andother nonplanar devices deliver better performance in a smallerfootprint than their planar counterparts.

With respect to the gate stack 112, it may include an interfacial layer114 where it meets the channel region, a gate dielectric 116, such as ahigh-K dielectric layer, disposed on the interfacial layer 114, and oneor more metal-containing layers 118 disposed on the gate dielectric 116.In various embodiments, the metal-containing layers 118 include acapping layer, a work function layer, a barrier layer, and/or anelectrode fill. Examples of these layers are shown and described in moredetail below.

The gate stack 112 may be disposed between a pair of opposing gatespacers 120. The gate spacers 120 may be used to control the size of thechannel region 110 by controlling where the source/drain features 108are formed and may be used in the formation of the gate stack 112. Insome embodiments, the workpiece 100 includes a gate seal 122 disposedbetween the gate spacers 120 and the gate stack 112. The gate seal 122may extend vertically between a vertical side surface of the gatespacers 120 and a vertical side surface of a component of the gate stack112, such as the gate dielectric 116.

The gate seal 122 may improve the fabrication of the workpiece 100 andspecifically the gate stack 112. In some examples, the gate seal 122 isformed by a process that produces a more uniform shape, particularlybetween fins, than the deposition used for the gate spacers 120. Thismay prevent portions of the gate stack 112 from extruding throughdefects in a gate spacer interface. In some examples, the gate seal 122reduces the surface roughness of a placeholder gate material that issubsequently replaced to form the gate stack 112. In so doing, the gateseal 122 may provide a better interface with the gate spacers 120 andmay further prevent gate stack extrusion. Similarly, in some examples,the gate seal 122 fills voids in the placeholder gate material toprovide a better shape for the subsequent gate stack 112. In theseexamples and others, the gate seal 122 improves the uniformity of thegate stack 112 leading to more reliable device performance and feweryield-killing defects.

Exemplary methods of forming a workpiece with a gate seal 122, such asthe workpiece 100 of FIG. 1 , will now be described with reference toFIGS. 2A-15B. In that regard, FIGS. 2A and 2B are flow diagrams of amethod 200 of fabricating a workpiece 300 according to some embodimentsof the present disclosure. The workpiece 300 may be substantiallysimilar to the workpiece 100 of FIG. 1 in many regards. Additional stepsmay be provided before, during, and after the method 200, and some ofthe steps described may be replaced or eliminated for other embodimentsof the method 200. FIGS. 3A, 4A, 5A, 6A, 7A, 8A, 9A, 10A, 11A, 12A, 13A,14A, and 15A are cross-sectional view diagrams of the workpiece 300taken through a fin 104 at various stages of the method 200 offabricating the workpiece 300 with a gate seal according to someembodiments of the present disclosure. FIGS. 3B, 4B, 5B, 6B, 7B, 8B, 9B,10B, 11B, 12B, 13B, 14B, and 15B are cross-sectional view diagrams ofthe workpiece 300 taken through a non-fin region at various stages ofthe method 200 of fabricating the workpiece 300 with a gate sealaccording to some embodiments of the present disclosure. Specifically,the figures show the formation of first and second portions of a singlegate stack 112 with a gate seal 122, although it is understood that thegate stack 112 may span multiple fins 104 and that the workpiece 300 mayinclude any number of such gate stacks 112. For clarity, some aspects ofthe figures have been simplified or omitted.

Referring first to block 202 of FIG. 2A and to FIGS. 3A and 3B, aworkpiece 300 is received that includes a substrate 102 with fins 104extending from it. In various examples, the substrate 102 includes anelementary (single element) semiconductor, such as silicon or germaniumin a crystalline structure; a compound semiconductor, such as siliconcarbide, gallium arsenic, gallium phosphide, indium phosphide, indiumarsenide, and/or indium antimonide; an alloy semiconductor such as SiGe,GaAsP, AlInAs, AlGaAs, GaInAs, GaInP, and/or GaInAsP; anon-semiconductor material, such as soda-lime glass, fused silica, fusedquartz, and/or calcium fluoride (CaF₂); and/or combinations thereof.

The substrate 102 may be uniform in composition or may include variouslayers, some of which may be selectively etched to form the fins. Thelayers may have similar or different compositions, and in variousembodiments, some substrate layers have non-uniform compositions toinduce device strain and thereby tune device performance. Examples oflayered substrates include silicon-on-insulator (SOI) substrates 102. Insome such examples, a layer of the substrate 102 may include aninsulator such as a semiconductor oxide, a semiconductor nitride, asemiconductor oxynitride, a semiconductor carbide, and/or other suitableinsulator materials.

The fins 104 may be formed by etching into the substrate 102 and/or bydepositing (e.g., epitaxially growing) material upon the substrate 102.Accordingly, the fins 104 may include some materials in common with thesubstrate 102 or may be entirely distinct in composition. In variousexamples, the fins 104 may include one or more layers of asemiconductor; a dielectric such as a semiconductor oxide, asemiconductor nitride, a semiconductor oxynitride, and/or asemiconductor carbide; and/or other suitable material.

The workpiece 300 may include isolation features 106, such as ShallowTrench Isolation features (STIs), disposed between the fins 104. Theisolation features 106 may include a dielectric such as a semiconductoroxide, a semiconductor nitride, a semiconductor carbide, FluoroSilicateGlass (FSG), a low-K dielectric material, and/or other suitabledielectric material. The dielectric material may be deposited by anysuitable technique including thermal growth, Chemical Vapor Deposition(CVD), High-Density Plasma CVD (HDP-CVD), Physical Vapor Deposition(PVD), Atomic Layer Deposition (ALD), and/or spin-on techniques. In onesuch embodiment, a CVD process is used to deposit a flowable dielectricmaterial that includes both a dielectric component and a solvent in aliquid or semiliquid state. A curing process is used to drive off thesolvent, leaving behind the dielectric material of the isolationfeatures 106 in its solid state. Referring back to FIG. 1 , theisolation features 106 may be recessed such that a portion of each finextends above the adjacent isolation features 106 while another portionof each fin is below and surrounded by the adjacent isolation features.

As noted above, the workpiece 300 may be fabricated in a gatereplacement or a gate-first process. In a gate replacement process, aplaceholder gate structure is first formed on the workpiece 300 andsubsequently replaced with a functional gate as described in blocks204-230. This may be done when materials of the functional gate (e.g.,gate electrode material, gate dielectric layer material, interfaciallayer, etc.) may be damaged by some fabrication processes, such asannealing.

Referring to block 204 of FIG. 2A and to FIGS. 4A and 4B, an interfaciallayer 114 is formed on the top and side surfaces of the fins 104. Theinterfacial layer 114 may include an interfacial material, such as asemiconductor oxide, semiconductor nitride, semiconductor oxynitride,other semiconductor dielectrics, other suitable interfacial materials,and/or combinations thereof. The interfacial layer 114 may be formed toany suitable thickness using any suitable process including thermalgrowth, ALD, CVD, HDP-CVD, PVD, spin-on deposition, and/or othersuitable deposition processes. In some examples, the interfacial layer114 is formed by a thermal oxidation process and includes a thermaloxide of a semiconductor present in the fins 104 (e.g., silicon oxidefor silicon-containing fins 104, silicon-germanium oxide forsilicon-germanium-containing fins 104, etc.).

Referring to block 206 of FIG. 2A and to FIGS. 5A and 5B, a placeholdergate material 502 is formed on the workpiece 300. The placeholder gatematerial 502 may include any suitable material such as a semiconductorand/or a dielectric. The placeholder gate material 502 may be formedusing any suitable process including CVD, HDP-CVD, PVD, ALD, spin-ondeposition, and/or other suitable deposition processes. In one suchexample, the placeholder gate material 502 includes polysilicon formedin a Low Pressure CVD (LPCVD) process using a precursor such as SiH₄ ata temperature between about 500° C. and about 650° C. and a pressurebetween about 0.2 Torr and about 1.0 Torr.

Referring to block 208 of FIG. 2A and referring still to FIGS. 5A and5B, a first hard mask layer 504 may be formed on the placeholder gatematerial 502 to aid in patterning the placeholder gate material 502. Thefirst hard mask layer 504 may include any suitable material, and invarious examples include a dielectric such as a semiconductor oxide, asemiconductor nitride, a semiconductor oxynitride, a semiconductorcarbide, etc. In one such example, the first hard mask layer 504includes silicon nitride. The first hard mask layer 504 may be formedusing any suitable process including CVD, HDP-CVD, PVD, ALD, spin-ondeposition, and/or other suitable deposition processes.

Referring to block 210 of FIG. 2A and referring still to FIGS. 5A and5B, a photoresist layer 506 is formed on the placeholder gate material502 and the first hard mask layer 504 and patterned to define aplaceholder gate 508. An exemplary photoresist layer 506 includes aphotosensitive material that causes the layer to undergo a propertychange when exposed to light. This property change can be used toselectively remove exposed or unexposed portions of the photoresistlayer in a process referred to as lithographic patterning. In one suchembodiment, a photolithographic system exposes the photoresist layer 506to radiation in a particular pattern determined by a mask. Light passingthrough or reflecting off the mask strikes the photoresist layer 506thereby transferring a pattern formed on the mask to the photoresistlayer 506. In other such examples, the photoresist layer 506 ispatterned using a direct write or maskless lithographic technique, suchas laser patterning, e-beam patterning, and/or ion-beam patterning. Onceexposed, the photoresist layer 506 is developed leaving the exposedportions of the resist, or in alternative examples, leaving theunexposed portions of the resist. An exemplary patterning processincludes soft baking of the photoresist layer 506, mask aligning,exposure, post-exposure baking, developing the photoresist layer 506,rinsing, and drying (e.g., hard baking). The patterned photoresist layer506 exposes portions of the first hard mask layer 504 and/or theplaceholder gate material 502 to be etched.

Referring to block 212 of FIG. 2A and to FIGS. 6A and 6B, the exposedportions of the first hard mask layer 504 and the placeholder gatematerial 502 are etched to further define the placeholder gate 508. Theetching processes may include any suitable etching technique, such aswet etching, dry etching, Reactive Ion Etching (RIE), ashing, and/orother etching methods. In some examples, etching includes multipleetching steps with different etching chemistries, each targeting aparticular material of the workpiece 300. In particular, the etchingsteps and chemistries may be configured to etch the first hard masklayer 504 and the placeholder gate material 502 without significantlyetching the fins 104 or the isolation features 106. Any remainingphotoresist layer 506 and/or first hard mask layer 504 may be removedfrom the placeholder gate material 502 after the etching.

Referring to block 214 of FIG. 2A and to FIGS. 7A and 7B, a gate seal122 is formed on the top and side surfaces of the placeholder gatematerial 502. The gate seal 122 may include any suitable material, suchas a semiconductor and/or dielectric. The gate seal 122 may be formed toany suitable thickness 702 and may be formed using any suitable processincluding thermal growth, CVD, HDP-CVD, PVD, ALD, High Aspect RatioProcess (HARP) and/or other suitable processes. In some examples, thegate seal 122 is formed by thermal oxidation of the placeholder gatematerial 502 and accordingly, contains an oxide of a material in theplaceholder gate material 502. In some examples, the placeholder gatematerial 502 includes polysilicon and is heated to a temperature atbetween about 700° C. and about 1500° C. in an environment containing O₂(dry oxidation), H₂O (wet oxidation), or other oxygen source. In onesuch example, the process produces a substantially conformal gate seal122 consisting essentially of polysilicon oxide (poly oxide) or othersuitable oxide with a thickness 702 selected to be between about 0.2 nmand about 2 nm. Accordingly, in examples where the placeholder gatematerial 502 has a thickness of between about 10 nm and about 20 nm anda height of between about 100 nm and 200 nm, the thickness of the gateseal 122 is between about 1/100 and 1/10 the thickness of theplaceholder gate material 502 and between about 1/1,000 and about 1/100the height of the placeholder gate material 502.

As noted above, the gate seal 122 may be formed using thermal growth,HARP, ALD, CVD, or other suitable processes. The particular process orprocesses may be selected based on the quality of the interface producedby the process in light of the surface roughness and other surfaceproperties of the placeholder gate material 502. A process may also beselected based on the uniformity of deposition at the bottom of narrowtrenches such as the non-fin regions between fins shown in FIG. 7B.Additionally or in the alternative, a deposition process may be selectedbased on the desired thickness of the gate seal 122. Accordingly, thepresent disclosure is not limited to any particular technique forforming the gate seal 122. In these examples and others, the gate seal122 reduces gate extrusion and other defects that may affect deviceperformance or yield.

Referring to block 216 of FIG. 2A and to FIGS. 8A and 8B, one or moregate spacer layers are formed on the gate seal 122 and the isolationfeature 106, of which three (an inner spacer layer 802, a middle spacerlayer 804, and an outer spacer layer 806) are shown. In variousexamples, each of the gate spacer layers includes a suitable material,such as: a dielectric material (e.g., a semiconductor oxide, asemiconductor nitride, a semiconductor oxynitride, a semiconductorcarbide, a semiconductor oxycarbonitride, etc.), SOG,tetraethylorthosilicate (TEOS), PE-oxide, HARP-formed oxide, and/orother suitable material. The gate spacer layers may be formed to anysuitable thickness using any suitable deposition technique (e.g., CVD,HDP-CVD, ALD, etc.). In one such embodiment, the inner spacer layer 802includes silicon oxycarbonitride, the middle spacer layer 804 includessilicon oxide, and the outer spacer layer 806 includes silicon nitride.In the embodiment, each gate spacer layer has a thickness between about1 nm and about 10 nm and is deposited by a conformal CVD and/or ALDprocess.

Referring to block 218 of FIG. 2B and to FIGS. 9A and 9B, the gatespacer layers are selectively etched to remove them from the horizontalsurfaces of the placeholder gate material 502, fins 104, and isolationfeatures 106 while leaving them on the vertical surfaces. This definesgate spacers 120 disposed alongside the placeholder gate 508. Theetching process may be performed using any suitable etching method, suchas wet etching, dry etching, RIE, ashing, and/or other etching methodsand may use any suitable etchant chemistries. The etching methods andthe etchant chemistries may vary as the gate spacer layers are etched totarget the particular material being etched while minimizing unintendedetching of the materials not being targeted. In some such examples, theetching process is configured to anisotropically etch the gate spacerlayers, while leaving the portions of the gate spacers 120 on thevertical sidewalls of the placeholder gate 508. In some embodiments, theetching process of block 218 is configured to remove the gate seal 122from the horizontal surface of the placeholder gate material 502 whileleaving the gate seal 122 on the vertical surfaces of the placeholdergate material 502.

Referring to block 220 of FIG. 2B and to FIGS. 10A and 10B, an etchingprocess is performed on the workpiece 300 to create recesses 1002 inwhich to form source/drain features. The etching process may beperformed using any suitable etching method, such as wet etching, dryetching, RIE, ashing, and/or other etching methods and may use anysuitable etchant chemistries, such as carbon tetrafluoride (CF₄),difluoromethane (CH₂F₂), trifluoromethane (CHF₃), other suitableetchants, and/or combinations thereof. The etching methods and theetchant chemistries may be selected to etch the fins 104 withoutsignificant etching of the placeholder gate 508, gate spacers 120, thegate seal 122, and/or the isolation features 106. In some examples, theetching of block 220 is performed as part of block 218.

Referring to block 222 of FIG. 2B and to FIGS. 11A and 11B, an epitaxyprocess is performed on the workpiece 300 to grow source/drain features108 within the recesses 1002. In various examples, the epitaxy processincludes a CVD deposition technique (e.g., Vapor-Phase Epitaxy (VPE)and/or Ultra-High Vacuum CVD (UHV-CVD)), molecular beam epitaxy, and/orother suitable processes. The epitaxy process may use gaseous and/orliquid precursors, which interact with a component of the substrate 102(e.g., silicon) to form the source/drain features 108. The resultantsource/drain features 108 may be in-situ doped to include p-typedopants, such as boron or BF 2; n-type dopants, such as phosphorus orarsenic; and/or other suitable dopants including combinations thereof.Additionally or in the alternative, the source/drain features 108 may bedoped using an implantation process (i.e., a junction implant process)after the source/drain features 108 are formed. Once the dopant(s) areintroduced, a dopant activation process, such as Rapid Thermal Annealing(RTA) and/or a laser annealing process, may be performed to activate thedopants within the source/drain features 108.

The source/drain features 108 may have any suitable shape, and in someexamples, the source/drain features 108 have a substantially u-shapedprofile where a vertical sidewall portion of each of the source/drainfeatures 108 is substantially aligned with an outer vertical surface ofthe gate spacer 120 (e.g., exterior surface of the outer spacer layer806). Furthermore in some examples, halo/pocket implantation isperformed on the substrate 102, and as a result, the source/drainfeatures 108 extend underneath the gate spacers 120.

Referring to block 224 of FIG. 2B and to FIGS. 12A and 12B, a ContactEtch Stop Layer (CESL) 1202 is formed on the workpiece 300. The CESL1202 may be formed on the source/drain features 108 and on theplaceholder gate 508, and in particular, on the vertical side surfacesof gate spacer 120. The CESL 1202 may include any suitable material,such as: a dielectric material (e.g., a semiconductor oxide, asemiconductor nitride, a semiconductor oxynitride, a semiconductorcarbide, a semiconductor oxycarbonitride, etc.), polysilicon, SOG, TEOS,PE-oxide, HARP-formed oxide, and/or other suitable material. In someexamples, the CESL 1202 includes silicon oxycarbonitride. The CESL 1202may be formed to any suitable thickness using any suitable depositiontechnique (e.g., CVD, HDP-CVD, ALD, etc.). In some examples, the CESL1202 has a thickness between about 1 nm and about 10 nm, and isdeposited by a conformal CVD and/or ALD process.

Referring to block 226 of FIG. 2B and referring still to FIGS. 12A and12B, an Inter-Level Dielectric (ILD) layer 1204 is formed on theworkpiece 300. The ILD layer 1204 acts as an insulator that supports andisolates conductive traces of an electrical multi-level interconnectstructure that electrically interconnects elements of the workpiece 300,such as the source/drain features 108 and the gate stack. The ILD layer1204 may comprise a dielectric material (e.g., a semiconductor oxide, asemiconductor nitride, a semiconductor oxynitride, a semiconductorcarbide, etc.), SOG, fluoride-doped silicate glass (FSG),phosphosilicate glass (PSG), borophosphosilicate glass (BPSG), BlackDiamond® (Applied Materials of Santa Clara, California), Xerogel,Aerogel, amorphous fluorinated carbon, parylene, BCB, SILK® (DowChemical of Midland, Michigan), and/or combinations thereof. The ILDlayer 1204 may be formed by any suitable process including CVD, PVD,spin-on deposition, and/or other suitable processes.

A chemical mechanical polish/planarization (CMP) process is performed onthe workpiece 300. The CMP process may remove some or all of the CESL1202 and the ILD layer 1204 from the top of the placeholder gatematerial 502, and may be followed by an etch back to remove anyremaining material from the placeholder gate material 502.

Referring to block 228 of FIG. 2B and to FIGS. 13A and 13B, theplaceholder gate material 502 is removed as part of a gate replacementprocess to provide a recess 1302 between the gate seal 122 and betweenthe gate spacers 120. Removing the placeholder gate material 502 mayinclude one or more etching processes (e.g., wet etching, dry etching,RIE) using an etchant chemistry configured to selectively etch theplaceholder gate material 502 without significant etching of surroundingmaterials such as the gate seal 122, the fin 104, the gate spacerlayers, the CESL 1202, the ILD layer 1204, etc.

Referring to block 230 of FIG. 2B and to FIGS. 14A and 14B, a functionalgate stack 112 is formed in the recess 1302 defined by removing theplaceholder gate material 502. In some example, this includes depositinga gate dielectric 116 on the interfacial layer 114 and along at leastsome of the vertical surfaces of the gate seal 122. The gate dielectric116 may include one or more dielectric materials, which are commonlycharacterized by their dielectric constant relative to silicon dioxide.In some embodiments, the gate dielectric 116 includes a high-kdielectric material, such as HfO₂, HfSiO, HfSiON, HMO, HfSiO, HfZrO,zirconium oxide, aluminum oxide, hafnium dioxide-alumina (HfO₂—Al₂O₃)alloy, other suitable high-k dielectric materials, and/or combinationsthereof. Additionally or in the alternative, the gate dielectric 116 mayinclude other dielectrics, such as a semiconductor oxide, semiconductornitride, semiconductor oxynitride, semiconductor carbide, amorphouscarbon, TEOS, other suitable dielectric material, and/or combinationsthereof. The gate dielectric 116 may be formed to any suitable thicknessusing any suitable process including ALD, CVD, HDP-CVD, PVD, spin-ondeposition, and/or other suitable deposition processes.

The gate stack 112 may also include a gate electrode disposed on andwithin the gate dielectric 116 that, in turn, includes layers such as acapping layer 1402, a barrier layer 1404, one or more work functionlayer(s) 1406, an electrode fill 1408, etc.

Referring first to the capping layer 1402, the capping layer 1402 may beformed on the horizontal and vertical surfaces of the gate dielectric116 in block 230. The capping layer 1402 may include any suitableconductive material including metals (e.g., W, Al, Ta, Ti, Ni, Cu, Co,etc.), metal nitrides, and/or metal silicon nitrides, and may bedeposited via CVD, ALD, PE CVD, PEALD, PVD, and/or other suitabledeposition process. In various embodiments, the capping layer 1402includes TaSiN, TaN, or TiN.

A barrier layer 1404 may be formed on the horizontal and verticalsurfaces of the capping layer 1402 in block 230. The barrier layer 1404may contain any suitable material, such as W, Ti, TiN, Ru, orcombinations thereof. Materials for the barrier layer 1404 may beselected based on their resilience to diffusion into the capping layer1402. The barrier layer 1404 may be deposited by any suitable techniqueincluding ALD, CVD, PE CVD, PEALD, PVD (e.g., sputtering), and/orcombinations thereof.

One or more work function layer(s) 1406 are formed on the horizontal andvertical surfaces of the capping layer 1402 in block 230. Suitable workfunction layer 1406 materials include n-type and/or p-type work functionmaterials based on the type of device to which the gate stack 112corresponds. Exemplary p-type work function metals include TiN, TaN, Ru,Mo, Al, WN, ZrSi₂, MoSi₂, TaSi₂, NiSi₂, WN, other suitable p-type workfunction materials, and/or combinations thereof. Exemplary n-type workfunction metals include Ti, Ag, TaAl, TaAlC, TiAlN, TaC, TaCN, TaSiN,Mn, Zr, other suitable n-type work function materials, and/orcombinations thereof. The work function layer(s) 1406 may be depositedby any suitable technique including ALD, CVD, PE CVD, PEALD, PVD, and/orcombinations thereof.

Finally, an electrode fill 1408 is formed on the work function layer(s)in block 230. The electrode fill 1408 may include any suitable materialincluding metals (e.g., W, Al, Ta, Ti, Ni, Cu, Co, etc.), metal oxides,metal nitrides and/or combinations thereof, and in an example, theelectrode core includes tungsten (W). The electrode fill 1408 may bedeposited by any suitable technique including ALD, CVD, PE CVD, PEALD,PVD, and/or combinations thereof.

Referring to block 232 of FIG. 2B, the workpiece may be provided forfurther fabrication. In some embodiments, this includes forming aself-aligned capping feature 1502 on the gate stack 112. Theself-aligned capping feature 1502 may aid in contact formation byelectrically isolating the gate stack 112 from a misaligned contact thatpartially overlaps the gate stack 112. Accordingly, the self-alignedcapping feature 1502 may include a dielectric or other suitableinsulating material and in an embodiment includes silicon oxynitride. Inone such example, the layers of the gate stack 112 including the gatedielectric 116, the capping layer 1402, the barrier layer 1404, the workfunction layers 1406, and the electrode fill 1408 are partially recessedusing one or more etching techniques and etchants configured to etch thematerials of the gate stack without significant etching of the gate seal122 and/or the ILD layer 1204. The self-aligned capping feature 1502 isdeposited in the recess via CVD, PE CVD, ALD, PEALD, PVD and/or othersuitable deposition process, and a CMP process is performed such that atop surface of the self-aligned capping feature 1502 is substantiallycoplanar with a top surface of the ILD layer 1204, the CESL 1202, thegate spacer 120, and/or the gate seal 122.

Thus, the present disclosure provides examples of a circuit device thatincludes a gate stack and a gate seal. In some examples, a methodincludes receiving a substrate having a fin extending from thesubstrate. A placeholder gate is formed on the fin, and first and secondgate seals are formed on sides of the placeholder gate. The placeholdergate is selectively removed to form a recess between side surfaces ofthe first gate seal and the second gate seal. A functional gate isformed within the recess and between the side surfaces of the first gateseal and the second gate seal. In some such examples, the forming of thefirst gate seal and the second gate seal includes performing a thermaloxidation process on a material of the placeholder gate. In some suchexamples, the material of the placeholder gate includes polysilicon andthe gate seal includes polysilicon oxide. In some such examples, theforming of the functional gate includes forming a gate dielectric withinthe recess, and the gate dielectric physically contacts an entirety ofthe side surfaces of the first gate seal and the second gate seal. Insome such examples, the forming of the placeholder gate further formsthe placeholder gate on an isolation feature disposed adjacent the fin,and the forming of the first gate seal forms the first gate seal on afirst portion of the placeholder gate disposed on the fin and on asecond portion of the placeholder gate disposed on the isolationfeature. In some such examples, an interfacial layer is formed on thefin, and the placeholder gate is formed on the interfacial layer. Insome such examples, the first gate seal and the second gate seal areformed on the interfacial layer. In some such examples, a sidewallspacer is formed alongside the first gate seal, and the sidewall spacerphysically contacts the first gate seal. In some such examples, adielectric layer is formed on functional gate. The dielectric layerextends between the side surfaces of the first gate seal and the secondgate seal.

In further examples, a method includes receiving a substrate having achannel region. A placeholder gate is formed on the channel region, andthe placeholder gate is oxidized to form dielectric gate seals on theplaceholder gate. A gate spacer is formed on the dielectric gate seals.The placeholder gate is replaced with a functional gate such that thefunctional gate is disposed between the dielectric gate seals. In somesuch examples, the placeholder gate includes polysilicon and thedielectric gate seals includes polysilicon oxide. In some such examples,the functional gate includes a gate dielectric and the gate dielectricphysically contacts the dielectric gate seals. In some such examples,the gate dielectric extends along an entire vertical surface of each ofthe dielectric gate seals. In some such examples, the substrate includesan isolation feature, and the dielectric gate seals are on the channelregion and on the isolation feature. In some such examples, thefunctional gate is on the channel region and the isolation feature, andthe replacing of the placeholder gate is such that a first portion ofthe functional gate on the channel region and a second portion of thefunctional gate on the isolation feature are disposed between thedielectric gate seals.

In yet further examples, a device includes: a pair of source/drainregions, a channel region disposed between the pair of source/drainregions, a gate stack disposed on the channel region, and a gate sealdisposed on a side surface of the gate stack. In some such examples, thegate seal includes a dielectric material. In some such examples, whereinthe gate seal consists essentially of polysilicon oxide. In some suchexamples, the device includes a gate spacer disposed on another sidesurface of the gate seal opposite the gate stack such that the gatespacer physically contacts the gate seal. In some such examples, thedevice includes an interfacial layer disposed on the channel region, andthe gate stack and the gate seal are disposed on the interfacial layer.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method comprising: forming a fin-shaped activeregion protruding from a substrate; depositing a placeholder gatematerial over the fin-shaped active region and the substrate; patterningthe placeholder gate material to form a placeholder gate structuredirectly over a channel region of the fin-shaped active region; treatingthe placeholder gate structure to convert a portion of the placeholdergate structure into a dielectric layer; forming a sidewall spacer alonga sidewall surface of the dielectric layer; and replacing a remainingportion of the placeholder gate structure with a functional gate stack.2. The method of claim 1, wherein the treating of the placeholder gatestructure comprises performing a thermal oxidation to the placeholdergate structure.
 3. The method of claim 1, wherein the dielectric layercomprises polysilicon oxide.
 4. The method of claim 1, wherein thedielectric layer includes a conformal thickness along top and sidewallsurfaces of the remaining portion of the placeholder gate structure. 5.The method of claim 1, wherein a ratio of a thickness of the dielectriclayer to a thickness of the placeholder gate structure is less than1/10.
 6. The method of claim 1, wherein the forming of the sidewallspacer comprises: after treating the placeholder gate structure,conformally depositing a gate spacer layer over the fin-shaped activeregion and the dielectric layer; and selectively etching the gate spacerlayer to remove portions of the gate spacer layer formed on horizontalsurfaces of the fin-shaped active region and the dielectric layer. 7.The method of claim 1, further comprising: after the forming of thesidewall spacer, removing portions of the fin-shaped active region notdirectly covered by the placeholder gate structure, the dielectriclayer, or the sidewall spacer to form source/drain recesses; and formingsource/drain features in the source/drain recesses.
 8. The method ofclaim 1, wherein the replacing of the remaining portion of theplaceholder gate structure with the functional gate stack comprises:selectively removing the remaining portion of the placeholder gatestructure without etching the dielectric layer and the sidewall spacerto form a gate trench; and forming the functional gate stack in the gatetrench.
 9. The method of claim 1, further comprising: forming aself-aligned capping layer on the functional gate stack, wherein asidewall surface of the self-aligned capping layer is in direct contactwith the dielectric layer.
 10. A method comprising: receiving aworkpiece comprising a gate structure engaging a semiconductor fin;forming a dielectric layer on top and sidewall surfaces of the gatestructure, wherein the dielectric layer does not extend along a topsurface of the semiconductor fin; after the forming of the dielectriclayer, conformally depositing a gate spacer layer over the workpiece;and etching back the gate spacer layer and the dielectric layer to forma gate spacer and a gate seal layer, respectively, wherein the gate seallayer is disposed between the gate spacer and the gate structure. 11.The method of claim 10, wherein the gate structure includes polysiliconand the gate seal layer includes polysilicon oxide.
 12. The method ofclaim 10, further comprising: after forming the gate spacer and the gateseal layer, replacing the gate structure with a functional gate stackcomprising a high-K dielectric layer.
 13. The method of claim 12,wherein the high-K dielectric layer extends along an entire verticalsurface of the gate seal layer.
 14. The method of claim 10, wherein thegate structure is isolated from the semiconductor fin by an interfaciallayer, and the interfacial layer comprises silicon oxide.
 15. The methodof claim 10, wherein the workpiece further comprises anothersemiconductor fin isolated from the semiconductor fin by an isolationfeature, wherein the gate seal layer is in direct contact with theisolation feature.
 16. A method comprising: receiving a workpiececomprising a first semiconductor fin isolated from a secondsemiconductor fin by an isolation feature; selectively forming aninterfacial layer on the first semiconductor fin without forming theinterfacial layer on the isolation feature; forming a placeholder gateengaging the first semiconductor fin and having a first portion directlyon the interfacial layer and a second portion directly on the isolationfeature; forming a dielectric layer extending along sidewall surfaces ofthe first portion and second portion of the placeholder gate;conformally depositing a gate spacer layer over the workpiece, whereinthe gate spacer layer is spaced apart from the first semiconductor finby the interfacial layer; etching back the gate spacer layer to removalhorizontal portions of the gate spacer layer to form gate spacersextending along sidewall surfaces of the dielectric layer; selectivelyremoving the placeholder gate without etching the dielectric layer andthe gate spacers to form a gate trench; and forming a functional gatestack in the gate trench.
 17. The method of claim 16, wherein thedielectric layer further extends along a top surface of the placeholdergate, and the etching back of the gate spacer layer further removes aportion of the dielectric layer that extends along the top surface ofthe placeholder gate.
 18. The method of claim 16, wherein the dielectriclayer is in direct contact with the isolation feature.
 19. The method ofclaim 16, wherein the etching back of the gate spacer layer furtherremoves a portion of the interfacial layer not covered by theplaceholder gate, the dielectric layer, or the gate spacers.
 20. Themethod of claim 16, wherein the gate spacer layer extends along and indirect contact with a top surface of the isolation feature.